The invention relates to a slide valve having a pressure or pump port, a reservoir port, at least one consumer port, a slide which is loaded by a spring force in the direction of a first position and can be moved into a second position counter to the spring force by means of an adjusting assembly, and via which one of the consumer ports can be connected to the reservoir port in the first slide position and to the pump port in the second slide position. A seat-controlled safety valve is arranged between the adjusting assembly and the slide, is loaded in the closing direction by the slide loaded by the spring force and, in the closed position, shuts off the adjacent open end of a longitudinal duct formed in the slide, which longitudinal duct is constantly connected, on the one hand, to the consumer port and, on the other hand, to the reservoir port via the opened safety valve when the slide is possibly blocked and not loaded by the adjusting assembly.
A corresponding slide valve having a single consumer port is the subject-matter of the German patent document DE 3,811,669 A1 and can serve for connecting a consumer, which is usually non-pressurized or connected to the reservoir, to the pressure source or pump in particular cases. For this purpose, the slide is moved into its second position counter to the spring force by means of the adjusting assembly. The subsequent return of the valve into its starting position, in which the relevant consumer is uncoupled from the delivery side of the pump again and connected to the reservoir again, can be effected via the return spring assigned to the slide. Due to the safety valve, the consumer is guaranteed to be uncoupled from the pressure source or pump even if the slide is blocked in the second position in the case of a malfunction possibly occurring, in particular as a result of contamination. Accordingly, pressure relief of the consumer is possible in any case as soon as the adjusting assembly departs from its position assigned to the second position of the slide.
A slide valve is known from German patent document DE 2,413,440 C2 which serves for controlling a double-action consumer and, for this purpose, in a first position connects a first port of this consumer to a pressure source or pump and connects a second port of this consumer to a pressureless reservoir or the like while, in a second position, the second port of the consumer is connected to the pressure source pump and the first port of the consumer is connected to the reservoir or the like. Furthermore, a neutral position can be set, in which both consumer ports are closed off, but are connected to one another by a pressure relief valve arrangement if a pressure difference of a given size between the consumer ports is exceeded. This pressure relief valve arrangement is arranged in a longitudinal duct of the slide.
In motor vehicles, in particular, it can be desirable to be able to use a pressure source or pump, which usually serves for supplying a main consumer, temporarily for operating a further consumer.
In this case, it should be guaranteed that this further consumer can, on the one hand, be loaded only by a limited pressure and, on the other hand, be reliably uncoupled from the pressure source or pump under all circumstances - with simultaneous connection to the pressureless reservoir or the like.
This object is achieved according to the invention by a slide valve of the type mentioned above in that a further consumer port is connected to the pressure port in the first slide position and is separated therefrom in the second slide position, in that the longitudinal duct constantly communicates via a radial bore in the slide with that consumer port which is connected to the pressure port in the second slide position, in that the longitudinal duct of the slide which is closed off at one end by the safety valve is closed off at the other end by an additional pressure relief valve which limits the pressure in the longitudinal duct with the safety valve usually being closed, and in that the outlet orifice of the pressure relief valve communicates with the reservoir port in all positions of the slide.
Due to this construction, the pressure in the longitudinal duct of the slide and thus the pressure at the consumer port constantly connected to the longitudinal duct is always limited to a predeterminable value, the pressure limiting being effected without moving the slide and thus without displacing the control edges of the slide. Accordingly, the response of the pressure relief valve cannot have any influence whatsoever on the pressure ratios at the other consumer which is not connected to the longitudinal duct of the slide.
Due to the pressure relief valve integrated in the slide, an extremely compact construction is achieved, a particular advantage being that the preferably central longitudinal duct of the slide which is already present in any case on the delivery side of the safety valve is also used at the same time for providing the connection paths required for limiting the pressure. Due to the arrangement of the pressure relief valve at the end of the slide facing away from the safety valve and the adjusting assembly, the lead path connecting the outlet orifice of the pressure relief valve to the reservoir can also be used for discharging leaking fluid flowing to this end of the slide.
Especially preferred embodiments wherein the longitudinal duct extends at least essentially up to the end of the slide facing away from the safety valve, and wherein the additional pressure relief valve is arranged in this end region have the particular advantage that the pressure relief valve is arranged outside the control edge region of the valve and the valve slide can thus be designed in this region virtually independently of the pressure relief valve and the otherwise customary slide paths, for example, can thus also be retained.
According to certain preferred embodiments, the longitudinal duct formed in the slide additionally also serves in a particularly advantageous manner for guiding the slide-type closing body of the pressure relief valve accommodated in this duct. The spring system of the closing body can be adjusted in respect of its spring force.
In certain preferred embodiments, the outlet orifice which an be shut off by the pressure relief valve opens out into a collecting space which can also serve, in particular, for discharging leaking fluid occurring during operation. The return spring system, which may be a compression spring, for example, loading the slide into its first position is also expediently arranged in this collecting space.
Due to the particularly advantageous design variant according to certain preferred embodiments, switchover can take place selectively by corresponding movement of the valve slide between two consumer ports which are alternately connected to the pump or uncoupled from the delivery side of the pump in each case. For this purpose, consumers of different types may be provided. In accordance therewith, at least one of the consumers can be constantly connected to the reservoir via a return so that separate pressure limiting is not required for this consumer in contrast to a consumer connected and supplied with pressure only on one side.
According to other preferred embodiments, two different consumers are preferably to be supplied alternately by a single pump. Accordingly, the pump port can be connected selectively via the consumer ports, for example, to a level control or a differential lock assigned to a drive axle of the relevant vehicle.
If the differential lock is to be supplied with pressure only in special cases and the level control is usually to be connected to the pump, the slide valve is expediently designed wherein the consumer port, which is connected to the pump port in the first slide position, can be connected to the level control and the consumer port, which is connected to the pump port in the second slide position, can be connected to the differential lock.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.